This invention relates to integrated circuits, and more particularly, to density transition zones surrounding circuits such as spiral inductors.
When inductors are formed on integrated circuits, it may be desirable to shield, insulate, or otherwise prevent stray magnetic fields from the inductor from reaching other components on the integrated circuit. Integrated circuit inductors are often formed in the upper layers of an integrated circuit's dielectric stack in order to maximize the distance between the inductor and the substrate. Dielectric stack layers that lie between the inductor and the substrate may be mostly or entirely filled with a dielectric material such as silicon oxide. As a result, dielectric stack layers in the vicinity of the inductor may have a lower metal density, or no metal density, and a higher oxide density compared to surrounding areas on the integrated circuit.
During integrated circuit fabrication, processes such as chemical-mechanical planarization (CMP), also known as chemical-mechanical polishing, may be affected by differences in metal density on the integrated circuit. As metal tends to be softer than oxide, regions with higher metal density may polish down faster than regions with lower metal density. As a result, dielectric stack layers in the vicinity of an inductor, having lower metal density, may be thicker than dielectric stack layers in surrounding areas on the integrated circuit.
Such non-uniformity in stack thickness may adversely affect components on the integrated circuit, especially in areas immediately adjacent to the inductor, where dielectric layers may rapidly transition from thicker to thinner layers. One common approach for addressing this issue is to designate a transition zone (also known as a “density transition zone) around the inductor. No active components are usually formed in the transition zone. Instead, metal layers in the transition zone have a certain amount of inactive metal fill (also known as “dummy metal” or “dummy fill”). The dummy metal ensures that metal layers in the transition zone have a metal density that is intermediate between that of the inductor and that of the surrounding regions that contain active components. The transition zone helps provide a smooth transition between the thicker dielectric stack layers of the inductor and the thinner dielectric stack layers in surrounding regions of the integrated circuit.
However, certain inductor and transition zone geometries may present a challenge in providing a uniform distribution of metal and dielectric materials within a transition zone. Such geometries may include transition zones with angles greater than 90 degrees, such as 135 degree angles. Conventional transition zones with these geometries have exhibited non-uniformities in their dummy metal patterns.